Core C Summary/Abstract: This analytical core is housed primarily at the Lamont-Doherty Earth Observatory of Columbia University and, through subcontracts, at McMaster University in Canada and the University of Manchester in the UK. The Biogeochemistry Core will generate data in support of biomedical Projects 1 (PI: Ahsan) and 2 (PI: Gamble), geoscience Projects 3 (PI: Bostick) and 4 (PI: van Geen), the Community Engagement Core (PI: Zheng), and the Research Translation Core (Co-PIs: Baptista and Chillrud) of the Columbia University Superfund Research Program (CU SRP). The generated data will include field and laboratory analysis of 15,000 groundwater samples for dissolved arsenic (As) and, where required, laboratory measurements of redox-sensitive elements Fe, Mn, S, and P, the major cations Na, Mg, Ca, K, and potentially toxic constituents Cr, Ni, Co, Cu, Zn, Mo, Cd, Sb, Pb and U. Other constituents of groundwater analyzed under Core C will include the anions Cl, Br, SO4 (sulfate), and F in 3,000 samples, dissolved organic carbon (DOC) in 3,000 samples, and reactive organic acids such as lactate and pyruvate in 150 samples. Core C will also support radiocarbon analysis of DNA/RNA isolated from 30 groundwater samples and phospholipid fatty-acids (PLFA) extracted from 30 aquifer sediment samples. The same 30 aquifer sediment samples will be analyzed by next-generation Illumina pyrosequencing methods to characterize microbial populations and metagenomics. The speciation As and Fe in 300 aquifer sediment samples will be determined by synchrotron-based X- spectroscopy (XANES and EXAFS). Finally, 1,000 aquifer sediment samples will be analyzed for bulk concentrations of Fe, As, Ca and other relevant elements by X-ray fluorescence.